Price of copper has been low for decades at about $1 per pound. Around the middle of 2000's, the price of copper began to rise significantly. In 2006, copper price took a major jump to about $4 per pound. Ever since this rapid price increase, copper theft has become rampant. Copper wires have been stripped out of overhead power lines, streetlights, traffic signals, vacant properties, parks, stadiums, parking lots, construction sites, telecommunication and power facilities.
In response to this huge theft problem, laws and regulations have been enacted such as those requiring people selling copper wire at scrap yards to be photographed and fingerprinted, their driver's licenses copied and requiring a wait period for payment. However, the lack of resources to monitor and enforce the laws renders them essentially ineffective. Some utility companies started to offer large rewards, painting or marking their copper wires, and switching to wires with less copper and posting signs that the new wires are not worth stealing. Some cities pour concrete over utility covers or weld them shut. However, the thieves continue to steal wires from the utilities, and break open secured utility covers. Some other cities turn on their streetlights all day, but could only deter the less skilled thieves. Surveillance cameras and placement of alarms on the wire pull boxes have also been considered and tested, but cameras can cover very limited range, and the enormous number of wire pull boxes and hand holes on the streetlights make it an economic challenge to implement these protection devices.
Lastly, anti-theft cable retainers have been developed, including one shown in U.S. Pat. No. 7,723,612, to clamp the electrical wires to the pole fixture and foundation. This approach, however, does not preclude a thief from cutting the wires between pull box to pull box, not to mention the large labor cost involved in installing the tens of thousands of cable retainers. The tried and trued approach of having vigilant citizens reporting suspicious activities or crime in progress is still of significant value, but it is not a reliable method to detect theft or even feasible in remote areas. In short, despite of the numerous efforts and attempts, wire theft remains largely an unsolved problem.
The subject invention can overcome the limitations of prior art approaches and it is relatively simple as well as highly cost effective. Before describing the invention, a general review of the common wiring systems and power controls methods is beneficial.
Electrical wires generally carry two types of current, AC (alternative current) or DC (direct current). In the AC category, for transmission efficiency, high power electrical lines typically use 3-phase AC. For long distance transmission, very high voltage is also used to further reduce the size of the transmission wires. 3-phase AC can transmit power through a 4-wire or 3-wire system; to save the cost of an extra wire, 3-wire 3-phase AC is very commonly used. For electrical applications, such as streetlights, it is typically single-phase and at a lower voltage than that of the power transmission lines. The very high voltage of transmission lines is typically stepped down to a lower voltage by a transformer before connecting to a service point of a group of electrical loads.
The wiring system of streetlights is a good example to illustrate how typical electrical services are distributed. The starting point is called a service point, which contains electrical gears to control and supply power to a number of streetlights, which may consist of dozens of light fixtures. A wire pull box is installed next to a service point enclosure where underground conduits are connected to each light fixture through a combination of main conduit branches and sub-branches. Sub-branches are connected to the main branches or other sub-branches in a daisy-chain or star configuration. A wire pull box is installed next to each light fixture. Alternatively conduits are stubbed out directly from the foundation of a fixture and with wire accessed through a hand hole at the base of a pole. Streetlights are connected either through a 2-wire or 3-wire system.
Inside a service point enclosure, in addition to the typical electrical gears such as circuit breakers, the main power control to all the lights connected to the service point is through a contactor, which is a relay with large contact points capable of passing through high currents to power a group of lights. The activation of the contactor is done electro-mechanically through a wire coil or electronically through a solid-state circuit. Since the activation current of the contactor is small, light current control devices such as a small manual switch, photocell or time clock can be used to control the entire group of lights at the service point. Although it is common that only one photocell or time clock is used to control all the lights in the group, there are also configurations in which each fixture has an individual photocell or control device. The key difference is that under a single control, the distribution wires are not energized if the main control is off, creating an intermittently energized wiring configuration. When an individual fixture has its own control device, the distribution wires are usually always energized. The intermittently energized wiring configuration creates unique challenges to wire protection, which will be discussed below.
There are more complicated wiring systems such as those used for industrial applications. An example is a conveyor belt system in a mining or aggregate plant operation. However, their basic wiring layout is very similar to those of the streetlight system mentioned above except that they typically use 3-phase AC instead of single phase, and their controls are not photocell or timer. Remote controls are generally used to control the power contactors of industrial electrical loads. Further, for controlling motors, the contactor device includes an overload relay; the combined unit is commonly called a starter.
The most common type of starter is full voltage, which behaves like the contactors in light control. Once an activation voltage is sent to the starter, the contacts close and power is transmitted to the motor. There are soft starters, which respond to varying control voltage or current, and then send various levels of line voltage down to the electrical load, such as a large heating element. Soft starters complicate the task for protecting electrical wires, but the subject invention can handle this situation easily as well. Depending on the design of a motor, if speed control is required, different wiring configurations are necessary to match the motor type, but it still follows a simple fact that the transmission wires are energized in some fashion in response to the control settings.
Besides AC power, DC power is also used to send power or signal down transmission wires. An example of DC application is telephone wires. In some applications, such as landscaping, both AC and DC are used, such as using low voltage AC for irrigation control circuits and low voltage DC for solar powered lighting.
For overhead power line protection, the challenge is presented by the miles and miles of continuous wires and it is difficult to quickly identify the location where the cables are cut so that action can be taken promptly. The lack of precise location for prompt response makes the overhead power lines another target for skilled wire thieves.
The above discussion summarizes the range of conditions and challenges for wire protection. Nonetheless, regardless of high or low voltage, AC or DC, the types of power control, the length of the transmission wires, and whether the wires are intermittently energized, the subject invention can protect the wiring systems cost effectively.